Method and means for eliminating fading



July 11, 1933. H. H. BEVERAGE ET AL 1,917,291

METHOD AND MEANS FOR ELIMINATING FADING Filed May 2, 1928 I291 7'0 RICE/VIP INVENTORS H. H. BEVERAGE AND 2-1.0v PETERsON ATTOR nanonn 1r. BEVERAGE Ann HAROLD o.

Patented July 11, 1933 STTE PATNT PETERSON,

ASSIGNORS TO RADIO CORPORATION OF AMERICA, A. CORPORATION OF METHOD AND MEANS FOR ELIMINATING FADING Application filed May 2,

This invention relates to the elimination of what has come to be known in radio signalling and speed transmission systems as fading. The invention as herein disclosed, is particularly adapted for use in the reception of'short wave radio signals and for use in locations where the efiiect of fading of signals is particularly troublesome, although it is to be understood that thesystem is likewise capable of efiicient use for all types of radio receiving systems, and is useful for long waves as well as short waves.

Considerable study in the art of short wave radio transmission and reception discloses the fact that diiierent locations have dilfercut-fading characteristics and it is, therefore, conceivable that signals received upon geographically separated antennae might be of a maximum intensity at any instant at one point and a minimum intensity at the same instant at the other point and at a later instant the conditions might be exactly the reverse. This same condition and state of affairs has been found to hold true with a plurality of antennae of difierent directivecharacteristics located at the samepoint and, while we will refer in this specification and claims to the use of geographically separated antennae for the purpose o'l describing and claiming our invention, it is'to be particularly understood that the invention relates also broadly to antennae of diil'erent directive characteristics located at the same point, wherein a horizontal doublet might correspond to one antenna: and a vertical doublet might correspond to a geographically spaced second antennae member, and in this last,

named arrangement both the horizontal and the vertical doublet would have dillerent directive characteristics.

An ideal condition for combining signals from various geographically spaced antenna systems would be to direct their separate energy to a common receiver and make a single adjustment for phase displacement of the various antenna systems relative to each other, but experimentation has proved that this system will hold great limitations inasmuch as it has been found that the phase relation ship between the signal voltage received at 1928. Serial No. 274,274.

ing signals from various geographically separatedantenna systems or from antenna systems having different directive properties located at the same'point, so that the signals from the various antenna systems may be combined independently of the phase rela tionship of the signals received on any sepa rate antenna system. The broad idea of this scheme of combining signals has been disclosed in our copending application, Serial No. 78,708, filed January 2nd, 1926, as 'well as application Serial No. 261,737, filed March 15th, 1928, of which this application repre sents a'modification and further development of the broad idea set forth.

We have illustrated diagrammatic embodiments which our invention may assume by the accompanying drawing, wherein:

are entitled to various modifications such as fall fairly within the spirit and scope of this invention, and We have resorted to the showing of the specific embodiments as illustrated by Figs. 1 and 2 of the drawing merely for the purpose of making a concrete illustration, but consider our invention as broad enough to all forms such as fall fairly within its scope as defined by the claims followciring the end of this specification.

7 To now make reference to Fig. 1 of the drawing, we have shown a receiving'system in which, for convenience of illustration, three antennae systems designated 1, 2 and 3 have been indicated. The energy picked up on each ofthe antennae systems 1, 2 and 3, which, as

above stated, may be geographically separate antennae or antennae located at a single point but having different directive characteristics, is carried through tuned circuits of any desired character such as d, 5 and 6 which are all tuned to the same signal frequencies.

V which are designated as 13,14: and to direct energy from the several vacuum tubes to a common receiving ClICLllQ'Q'GHQZ'LlllY designated 16, wh1ch is connected with a common 7 receiver (not shown).

The grid returns from the several vacuum tubes, 10, l1 and 12 arelthen carried to several points 17, 18 and 19 on, an artificial line, generally designated 20. The artificial line 20 preferably consists of series inductance 21 and shunt capacity 22. The capacity elements 22 are associated with a common side of the artificial line which is grounded at 23 and with the inductance element 21. The artificial line is substantially a wave length long electrically for a particular oscillator frequency to be hereinafter described, although it is to be understood that this limitation is unnecessary. The capacity elements 22 constitute the capacity elements of this artificialline. Connected across the end of the artificial line 20 is a damping resistance 24 for the purpose of damping reflections which might be possible upon the line.

Coupled to the artificial line 20 through any desired form of coupling connection, as by the transformer 25, is an oscillator 26 'which is preferably of, the low frequency type, and may be either an audible frequency or a superaudible frequency.

As has been above stated, the grid returns of the vacuum tubes 10, 11 and 12 are connected to the artificial line at 17, 18 and 19. These difi'erent points of connection to the artificial lines may or may not be nodal points on the artificial lines,'but preferably may be chosen as any point desired, of course, assuming that the artificial line is 360 electrical degrees long for the particular frequency of the oscillator 26. 'l Vhere the line 20 is 360 degrees long the points of connection of the grid return leads preferably will be spaced substantially 120 electrical degrees apart, but here again this spacing'of points is not essential to the operation of the invention, and the spacing may be of any desired separation along the artificial line regardless of how close or remote from a succeeding point.

The oscillator 26 which is coupled to the artificial line produces travelling'waves down the artificial line toward the direction of the damping resistance 24, and it is readily seen that these traveling waves might at one instant give a maximum positive voltage at the grid return connection point 17 for the grid 7 of the tube 10, and at the same instant would be almost minimum or negative voltage at the grid return connections 18 and 19 of the tubes 11 and 12. This would mean at this particular instant a'considerable amount of energy would be transferred to the output circuit of the tube 10 and very little energy would be found in the output circuit of the tubes 11 and 12, since under normal conditions the biasing batteries 27, 28 and 29 associated with the tubes 10, 11 and 12 respectively bias'the grid ele1nents7, 8 and 9 to cut-01f, but with the point 17 as grid connection of the tube 10 to the artificial line 20, becoming strongly positive, the tube 10 will no longer be biased to cut-off and with said positive bias on the grid 7 the tube will continue to pass plate current until the maximum positive voltage of the oscillator is removed from point 17 and the cut-off potential again applied to the grid from the C battery. However, at the next instant after the point 17 connection of the grid return from tube 10 has been subjected to the maximum positive voltage on-the artificial line a maximum posi tive voltage might be found at point 18 of connection of the grid return tube 11 to the artificial line, under which condition the bias battery 28 upon the grid 8 of the tubes 11 will be overcome and the tube 11 will com- 'mence to pass )late current and the signal received upont e antenna tube and selected through the tuning means generally designated 5 .willbe transferred through the tube 11 and the coupling or transformer 14 through the circuit 16 which connects with the receiving system in a manner similar to that above set forth in regard to tube 10 and its associatcd antenna system 1. At this same period of time the points 17 and 19 for connecting the tubes 10 and 12 to the artificial line will not be at a positive value but will be ap proaching a minimum value and the bias batteries 27 and 29 of the tubes 10 and 12 will control the grid potentials so that the tubes will be biased to cut-off. Under conditions when a maximum positive voltage attains at point 18 the tube 11 will be the only tube to transfer energy to the receiving system.

Under similar conditions at a later instant the point- 19 will be at a maximum positive voltage and the points 17 and 18 will be at less positive voltages, so that in a manner similar to that described in connection with tubes 10 and 11 the tube 12 will transfer energy from the antenna system 3 through the coupling transformer to the circuit 16 of the receiving system, and at the same time the tubes 10 and 11 will be biased to cut-off.

It is thus seen that the outputs of the tubes 10, 11 and 12 are all coupled inductively with the input circuit 16 of a common receiving system, so that maximum energy from tube 10 willbe transferred to the common receiving system at one instant, then at a later instant maximum energy from tube 11 and at a still later instant maximum energy from tube 12, and following with tube 10 in the manner described. These maximums periodically change so that irrespective of the phase relationship of the radio frequency energy picked up on the separate antenna systems 1, 2 and 3 the energy is directed to the common receiving means and the effects of fading and phase relationship are no lou er detrimental and the energy can be combined absolutely and totally independent of any phase relationship of the signals at the various antennae.

By Fig. 2 of the accompanying drawing u'e have shown a system which is a modified form of that shown by Fig. 1. By Fig. 2, in a similar manner to that shown by Fig. 1, signal energy is received and the cally spaced antennae systems or upon antcnna systems of difierent directive characteristics located at a common point, which have been designated 101, 102 and 103 respectively. The energy received upon the antenna systems 101. 102, 103 is directed through any preferred or desirable form of tuned circuit 104.. 105. 106 to the input electrode 107, 108. 109 of the vacuum tubes 110, 111 and 112 which each direct their output energy to a common receiving circuit 113 which is connected with a single receiving means (not shown). The output circuit of the tubes 110. 111. 112 embodies the primary winding of the coupling transformers, 114, 115 and 116 which are each associated with any desired form of-plate supply energy indicated as +B. Each of the vacuum tubes 110. 111. and 112 has a bias battery designated 117. 118 and 119 respectively connected in the grid return lead.

In a manner similar to that above described in connection with the artificial line. the batteries 117,, 118 and 119 in the grid return circuit of the tubes 110, 111 and 112 normally bias the grid member of these tubes down to cut-off so that. under normal condi-' tions, no signals are transferred from the antenna systems 101, 102, 103to the combininq' circuit 113 leading to the receiving apparatus for all of the antenna systems.

In contrast to the artificial line system and. its associated modulator shown by 1 for controlling the various tubes associated with the receiver and adapted to transfer radio frequency energ to the common com bining circuit, by Fig. 2 we have shown connections at 120, 121 and 122 for connecting geographi I the terminals .or leads connecting the ter minals of a'three phase oscillator of any desired character, and connected from the terminals 120, 121 and 122 in the form of a delta shaped net work. The windings 123, 124v and 125 form the primary winding of the transformers 126, .127 and 128 respectively. The secondary windings 129, 130 and 1310f the transformers 126, 127 and 128, respectively, are connected. and form a part of the arid return circuit of the tubes 110., 111 and 11.2, respectively. It is thus clearly seen that one phase of the three phase oscil ator is associated with the tube 110, another phase withthe tube 111 and the third phase with the tube 112.

When voltage is induced in the grid circuit of the tube through the secondary 129 of the transformer due to the fact that phase number one of the three phase oscillator is at a maximum positive point in its value, the tube 110 will function normally and the bias 117 which normally prevents plate current flow is overcome so that the grid member 107 is no longer biased to cut--. off and the tube functions normally and amplifies the radio frequency energy input from the antenna system 101 and passes this energy on through the common receiver by means of the output transformerlll which has its sec ondary winding, as above described, associated with the common combining circuit 113 for all of the various tubes in the system and forming a secondary winding in series with the secondary winding of the output transformer associated with the vacuum tubes 111 and 112. At the instant when the voltage induced inthe secondary 129 of the transformer 126 reaches a maximum value, the voltage induced in the secondary windings 130 and 131 of the so as to influence the grid members 108 and 109 of the tubes 111 and 112 will approach minimum value due to the local three phase oscillator. because of the fact tiat in the three phase system of supply, the voltage vectors are 120 electrical degrees apart. In this case, therefore, there is maximum radio frequency energy being passed through the tube" 110 and very little energy o1- noneat all being passed through the tubes 111 and 112 due to the fact that the voltage induced in the secondaries 130 and 131, above named, being of a minimum value and the bias in batteries 118 and 1.1.0 being suiticient to bias the tubes to cutoff. V 1

In a manner similar to that described in connection with tube 110, at some time after, the voltage induced in the grid circuit of tube 110 reaches a maximumvalue the voltage on the grid 108 of the tube .110 will be of a maximum value and tube 111 will then pass maximum energy to the common combining circuit 113andthe tubes 110 and 112 will pass minimum energy or none at all transformers 127 and 128 tion in a similar manner to connection with the artificial line of Fig. 1.

because of the bias applied, in a similar manner to that above described, because of the fact that the voltage induced in the grid circuit of the separate tubes are still 120 electrical degrees apart. Similarly, at a later instant the tube 112 will pass maximum energy to the combining circuit and the tubes 110 and 111 will pass minimum energy, after which the tube 112 passes energy to the con1- bining circuit the tube 110 will then be free to pass its maximum energy and the circle of operation will be continued.

hen the voltage induced in the grid circuit 107 of the tube 110 due to the local three phase oscillator reaches its maximumnegative value, it will aid the C battery 117 in biasing the tube 110 to cut-off so that no radio frequency energy will pass through the tube 110 and its associated output transformer 114 so as to direct itself to the common combinino' circuit 113. In a similar manner when the voltage from the three phase oscillator reaches a maximum negative value in the coils 124 and 125 the g *ids of the tubes 111 and 112 will be similarly biased to cut-off, since this maximum negative voltage 'Will aid the C batteries 118 and 119 respectively and their radio frequency output will be furnished from the tubes 111 and 112 in a similar manner to that described in connection with tube 110.

It is, therefore, readily apparentthat in the case last described of the three phase oscillator that the grids of the tubes may be periodically biased so that the three input tubes 110, 111 and 112 will be biased to cutoff and at first, one tube will pass maximum energy, then the next one Will pass maximum energy, and lastly the third tube will pass maximum energy through to the common receiving system, and the input signal phase will be entirely dissociated. It is readily seen. therefore, that this system will functhat described in In this case also, it is immaterial what the phase relationship of the radio frequency signal. energy upon the antenna 101, 102 and 103 may be, since the signals can, as has been above described, be combined absolutely independent of the phase relationship.

\Vhile we have described the system of Fig. 1 and the system of Fig. 2 as applicable to three geographically spaced antennae spaced at the same point, but having different directive characteristics it will be ap parentthat the system may be used for two antenna systems or more than three antenna systems by appropriate correction of the number of phasesfor the oscillator of Fig. 2, or appropriate positioning of the contact point for the grid return circuits of Fig. 1 to the artificial line 20 and, therefore, the system is one which readily lends itself to any number of antenna systems as may be chosen and be desirable.

It, therefore, can be understood that our invention is not restricted to the concrete examples which may be assumed from the drawing; and is not limited and should be understood in its broadest terms, and it should be apparent that it is through schemes for eliminating the detrimental effects of fading that commercial operation of communication on short wave length is made possible,

therefore, we wish our invention to be limited only in so faras it is necessary to limit the same from the scope of the following claims:

Having now described our invention, what we claim and desire to secure by Letters Patent is:

1. lhe method of avoiding the efiects of fading onradio signals which includes, re, ceiving the same signals at a plurality'of points and producing therefrom a plurality of signal effects, directing the said signal ef fects toa common receiving system for all of said receiving points, and continuously cyclically and consecutively associating each of said receiving points with said common receiving system.

2. Apparatus for avoiding the effects of fading on radio signals which includes, a plurality of antennae for receiving the same s1gnal, each of said antennae having different instantaneous response characteristics to the same signal effects, a common receiving point, means fordirecting the energy from said receiving point to said common receiving point, and means for continuously cyclically and successively associating one of said points with said common receiving point.

3. The method of overcoming fading efie'cts when receiving radio signals with receiving antennw of different instantaneous response characteristics and a radio frequency combining circuit which comprises, receiving the same signal bearing waves upon each of said antenna systems to produce a plurality of radio frequency signaling effects, continuously and successively associating each of said antenna systems with said radio frequency combining circuits, deriving signals in said combining circuit from said different antenna systems at successive and predetermined periods from each oi. said antenna systems, combining said derived signals and obtaining the transmitted signals from the combined signals. r

4. The method of avoiding the effects of fading of radio signals which includes, receiving the same signal at a plurality of receiving points each exhibiting different in stantaneous response characteristics to the same signal, producing from said received signals a plurality of signal effects, introducing to each of said produced signal effects the effects of a low frequency, and alternatively and successively associating each of said receiving points with-a common receiving system, and interrupting the association of each of said separated receiving points with said receiving system at said low frequency rate.

5. The method of avoiding the effects of fading on radio signals which includes, re-

ceiving the same signal at a plurality of points of dilferent instantaneous response characteristics and producing therefrom a plurality of signal effects, associating each of said plurality of points with a common receiving system for all of said reception points, biasing each of said receiving points nor mally to cut-off, removing said cut-off bias from said points successively and continuously at a low frequency rate,and receiving the effect from the signal as received at said plurality of points interruptedly and successively in said common receiving system.

6. The method of avoiding the effect of fading on radio signals which includes, receiving the same signal at a plurality of points of difierent instantaneous response characteristics and producing therefrom a plurality of signal effects, associating eachof said plurality of points with'a common receiving system for all of said receiving points, normally biasing each of said receiving points to cutoff, removing said cut-off bias from said point successively and continuously at an audible rate, and receiving the effect of the signal as received at said plurality of points intcrruptedly and successively in said common receiving system.

7. A system for the elimination of fading on short wave lengths which i cludes, a plurality of receiving means of different instantaneous response characteristics, a receiving circuit associated with each of said receiving systems and adapted to combine the energy from all of said systems, means for biasing each of said receiving systems normally to cut-off, and means for alternatively and successively removing the bias from said receiving systems and associating in succession said receiving means with said receiving circuit.

8. A system for the elimination of fading which includes, a plurality of receiving antennae each having different instantaneous response characteristics to the same signal effect, a vacuum tube amplifier for transferring the efiect received upon each of said antenna systems, a common receiving circuit for all of said antenna systems, said receiving circuit being associated with the output of all of said vacuum tube amplifiers, means for normally biasing each of said amplifiers to cut-01f, and means for successively and I continuously removing the bias from one of said amplifiers, whereby said amplifier passes received signal energy to said combining circuit and the remainder of said amplifiers are blocked with respect to the received signal energy and at each instant only one of said amplifiers is associated with saidreceivingcircuit. i

9= A system'for the elimination of fading which includes,a plurality of receiving antenne each having different instantaneous response characteristic to the same signal effeet, a vacuum tube amplifier'for transferring the signal effects received upon each of said antenna systems, a common receiving circuit. for receiving the signals from all of said antenna systems, a coupling means for associating said receiving circuit with the output of all of said vacuum tube amplifiers, means for normally biasing each of said amplifiers to a cut-off potential, and means for successively and continually removing the said cut-01f bias from one of said amplifiers at a low frequency rate, whereby said amplifier passes received signal energy to said common receiving circuit and the remainder of said amplifiers are blocked with respect to the received signal energy and at each instant only one of said amplifiers is associated with said receiving system.

10. A system for eliminating'the efiects of fading of signals in radio signalling apparatus which includes, a plurality of receiving antenna systemseach having difierent instantaneous response characteristic to the same signal, a single receiving circuit for all of said antenna systems, a vacuum tube relay system ,for coupling each of said antenna systems with said single receiving system, means for normally maintaininga cut-off bias potential upon each of said vacuum tube relays, means for cyclically removing said cut-olfbias potential from said rela'ys and simultaneously associating each of said antenna systems and associated relays and its associated relay with said receiving circuit. I I y i l1. A system forthe elimination offading of signals in radio signalling apparatus which includes, a plurality of receiving antenna systems each having different instantaneous response characteristic to the same signal, a'vacuum tube relay system associated with each of said antenna systems, a single combining circuit for all of said antenna systems inductively associated with the output of each of said vacuum tubes, means for biasing the input electrode of each of said vacuum tubes to a predetermined cut-ofi potential, an artificial line, a connection between the grid electrode of each of said vacuum tubes and a point on said artificial line, a low frequency oscillator inductlvely coupled with said artificial line for producing wave trains propagating the length of said artificial line and means provided by said oscillator for successively and continuously applying a positive potential bias to the grids of said tubes for overcoming the cut-off bias and successively and continuously associating each of said vacuum tubes wlth sald common receivmg system,

whereby the effects of fading are substantially reduced in said receiving system.

12. A system for the elimination of fading of signals in radio receiving apparatus which includes a plurality of receiving antennae of different instantaneous response characteristics, an amplifier associated with each of said antenna systems, a common receiving circuit for receiving the signal effects from all of said antenna systems, means for coupling each of said amplifiers with said common receiving circuit, means for normally maintaining a cut-off potential upon each of said amplifiers, whereby signal energy reaching each of said amplifiers is bloc red from said common receiving circuit, an oscillator and means for associating each of said amplifiers with said oscillator whereby the cut-off bias potential is cyclically and successively removed from each of said amplifiers and the said amplifiers successively pass signal energy into said common receiving circuit and the signals received upon said plurality of antennae are combined in said receiving circuit independent of the phase relationship at the antenna and the effects of fading are substantially eliminated. v

13. The method of overcoming fading effects during signalling which includes collecting in characteristically different fashions signal bearing transmitted energy at a plurality of separated points, and continuously and in predetermined sequence translating the energy collected at each point in order to obtain the transmitted signal.

14. The method of overcoming fading effects during signalling which includes collecting signal bearing energy at a plurality of separated points, producing potential waves, utilizing the waves produced to control the successive translation of the energy collected at each of the points, and combining the translated energy to obtain the 'transmitted signals.

' r 15.. The method of reducing fading during radio signallingv which includes collecting electromagnetic energy of like frequency at a plurality of points and translating successively and in predetermined order the energy collected at each point.:

16. The method of reducing fading during radio signalling which includes collecting electromagnetic energy of like frequency at a plurality of separated points, and translating successively and continuously in predetermined order the energy collected at each point automatically. 7 v

17. The method of reducingfading during radio signalling which includes collecting electromagnetic energy of like frequency at a plurality of separated points and translating successively at a supersonic frequency th energy collected at each point.

18. Radio signalling apparatus for overcoming fading of signal bearing radio waves comprising means for collecting electromagtermined order translating the energy collected at each point, and means for deriving transmitted signals from the translated energy.

20. Radio signalling apparatus comprising means for collecting electromagnetic energ of like frequency at a plurality of separated points and means for translating successively at a supersonic frequency the energy collected at each point.

HAROLD H. BEVERAGE. HAROLD O. PETERSON. 

